1. Field of the Invention
The present invention relates generally to a method and device for monitoring combustion in a furnace, such as a blast furnace, shaft furnace, reducing furnace or the like. More specifically, the invention relates to a method and device suitable for invention relates to a method and device suitable for monitoring temperature distribution and for sampling gases in a raceway adjoining the tuyere of the furnace.
2. Description of the Prior Art
For many years, there has been desire to monitor the behaviour of molten bodies near the tuyere or melting region in metallurgical furnaces, such as blast furnaces, shaft furnaces, reducing furnaces and so forth, in order to identify the cause of melt-down of the tuyere or formation of pool of molten material in front of the tuyere.
This is especially necessary for effective and efficient control of the composition of molten pig iron. A recently developed technique involves injecting iron ore and pulverized coal into the furnace through the tuyere. The charge injected through the tuyere reacts with the molten pig iron dripping through the coke burden and so changes the composition of the molten pig iron. The composition of the molten pig iron could be controlled only by analysing the mechanism and rate of the reaction between the charge and the molten pig iron. To do this, it would be necessary to measure the temperatures of and to sample the melt and the gas not only in the raceway but also in the central portion of the furnace which is filled with coke.
However, the central portion of the operating furnace is at a very high temperature and is subject to an accordingly large thermal load. This and the presence of the coke burden itself have previously made it difficult to insert a sensor probe into the central portion of the furnace while the furnace is in operation.
In the prior art, there is a raceway probe for monitoring gas composition and gas temperature in the raceway. A raceway probe is disclosed in Japanese Patent First Publication (Tokkai) Showa 58-16005 and the Japanese Utility Model Publication (Jikko) Showa 59-28027. In the aforementioned Japanese Publications, the raceway probe comprises a water-cooled tube inserted into the raceway near the tuyere of the furnace for monitoring gas composition and gas temperature. The probe is inserted into the furnace through a blow pipe and through the tuyere to monitor temperature, gas composition and so forth. The probe must be more than 3 meters long for successful monitoring. The internal diameter of the blow pipe is about 150 mm. Therefore, the orientation of the probe is limited to near that of the axis of the blow pipe, which is essentially radial. This limits the range of monitoring. Furthermore, when the probe is inserted through the blow pipe to monitor combustion conditions, the cross-sectional area of the blow pipe becomes more constricted, which significantly affects combustion.
In order to minimize the adverse affect on the blow pipe cross-section, the external diameter of the probe can be reduced to about 50 mm. However, in that case, the rigidity of the probe would be insufficient to ensure that the tip of the probe reaches the central portion of the furnace. Furthermore, the probe in the blow pipe is subject to very high temperatures, e.g. 1000.degree. C. to 1300.degree. C. Consequently, the probe may sustain approximately half of the total thermal load within the blow pipe. This necessitates a very-large-capacity water-cooling pipe. For instance, when the thermal load is doubled, the water-cooling pipe capacity must also be doubled to handle twice the cooling water.
Furthermore, it cannot be ignored when considering the accuracy of the monitoring that the presence of probe and the monitoring operation themselves will affect combustion conditions.
As can easily be appreciated, the disadvantages of the conventional probe reside in the presence of the probe within the blow pipe. Therefore, most of the disadvantages in the conventional probe can be eliminated if the probe can somehow be inserted into the furnace without passing through the blow pipe.
In this regard, an improved combustion condition monitoring system has been proposed in Japanese Patent Application Showa 59-69217 which has been published under No. 60-213845, and which was filed by the owner of the present invention. The prior proposal made in the foregoing Japanese Patent Application has a rather complicated structure and thus is very expensive.